For improving and modifying physical properties of starch, heretofore, there was known a method of adding an .alpha.-amylase or acid to starch, when starch is blended with water for gelatinization, so as to lower the viscosity of the blend. There was also known a method of adding various substances such as a metal ion, an algal polysaccharide or a water-soluble gum to starch so as to elevate or lower the physical properties of the starch gel. For modifying the characteristics of starch granules, there was known a method of crosslinking starch granules to make the starch granules less soluble.
However, a method has heretofore been unknown, in which starch granules are directly treated with an enzyme to modify the characteristics of the granules, whereby the physical properties of the granules are noticeably varied when dissolved in water. It was heretofore not known how greatly the physical properties of starch granules would vary when the starch granules are dissolved in water when they are treated with enzymes of certain kinds. It was heretofore not known that the physical properties of starch granules would vary greatly by such treatment.